1. Technical Field
The present invention relates to a portable device and, in particular, to a portable device such as a portable phone, a PDA (Personal Digital Assistance), and a notebook personal computer, provided with a connection section for connecting a plurality of housings in such a manner that their relative position can be changed.
2. Description of the Background Art
In recent years, in portable devices such as portable phones, PDAs, and notebook personal computers, compact and thin devices are strongly desired for the easiness of carrying. Thus, in portable phones and notebook personal computers, such devices are commonly used that a plurality of housings can be folded up through a hinge portion of a thickness of 10 mm or the like so that portability is improved.
Further, improvements from the perspective of multifunction, high performance, and the like are remarkably seen in these portable devices. As for portable phones, rapidly progressing improvements include: equipping with a camera having an image sensor of over megapixels; employing a high definition and large display; and installing a television function. These improvements cause a significant increase in the required signal transmission speed in the portable devices.
In the configuration of a portable phone used commonly, a body part generally provided with a key operation section and a control section is joined through a fold-up hinge with a cover part provided with a display and a camera. In the prior art, signal transmission between these body part and cover part has been performed by means of electric signals through a few tens or more of coaxial cables.
Here, in spite of the increase in the required signal transmission speed in the devices, the space for the hinge portion tends to decrease in order to satisfy the requirement of thickness reduction. This places a limit to the increase in the number of coaxial cables, and hence has caused a limit to the achievable signal transmission speed. Further, electromagnetic interference in the electric signals occurs between the antenna and the coaxial cables in the hinge portion, and thereby has caused a problem in speech quality and calling reliability.
In order to resolve these problems, the use of optical wiring in signal transmission has been proposed so as to achieve high speed signal transmission and mass data transmission between the body part and the cover part. For example, patent document 1 discloses that optical fibers are used as inter-housing transmission means and thereby achieve high speed transmission and suppress electromagnetic interference.
On the other hand, patent documents 2 and 3 disclose that film-shaped optical waveguides are used in optical wiring so as to interconnect boards. Patent document 2 discloses that a plurality of parallel signals outputted from a printed board are converted directly into a plurality of parallel optical signals, and then transmitted through film-shaped optical waveguides of the same number as the signals.
Patent document 3 discloses that core sections and a clad layer of optical waveguides, as well as metallic wiring, are formed on a polyimide film so that a flexible electro-optical wiring film is produced. Then, electro-optical devices mounted on electro-optical wiring boards are interconnected using the wiring film.
Patent document 1: Japanese Laid-Open Patent Publication No. 2003-244295 (p. 4, FIGS. 1 and 2).
Patent document 2: Japanese Laid-Open Patent Publication No. 01-166629 (pp. 2–3, FIGS. 1 and 2).
Patent document 3: Japanese Laid-Open Patent Publication No. 06-222230 (pp. 3–5, FIGS. 2 and 9).
Nevertheless, in the case of optical fibers disclosed in patent document 1, when the optical fibers are made of glass, the fibers break and become disconnected when their bend radius becomes small. In contrast, when these optical fibers are made of plastics having flexibility, their diameter becomes larger. Thus, when the bend radius in the hinge portion becomes small, light is no longer confined owing to the bending. That is, when the fold-up portion is closed, or in the course of the folding up, high speed transmission is not achieved. This places a notable restriction on the use of the device. In order to reduce this optical loss, when the fibers made of plastics were constructed such as to be bent in a larger bend radius, the device thickness in a folded-up state could increase so as to cause a problem in the portability.
Further, in the disclosures of patent documents 2 and 3, major attention is focused on the point that the flexibility of the film-shaped optical waveguides allows the interconnection of boards arranged at different elevation or position from each other. That is, the film-shaped optical waveguides are not expected to be extremely bent or folded up into a bend radius of as small as 5 mm or even less, as is the case with a portable device. Further, in the disclosures of these two patent documents, film-shaped optical waveguides are formed on a base film. This approach causes an increase in the total thickness of the base film and the film-shaped optical waveguide layer. Thus, when the bend radius becomes small, the optical loss increases.
On the other hand, in a portable device, a power supply such as a battery is arranged in one housing, while its supply voltage is provided to the other housing so that component devices in the other housing are driven. Nevertheless, patent document 1 discloses that the housings are connected through signal lines composed of optical fibers, but does not describe that a supply voltage is provided from a housing to another. Thus, when the signal lines described in patent document 1 are applied to a portable device, metallic wiring needs to be provided in addition to the optical fibers. Thus, as a whole, thickness reduction is not sufficiently achieved in the connection section.